GB882787A - Cabin pressurization system using a-c power - Google Patents

Abstract

882,787. Automatic pressure control systems. KOLLSMAN INSTRUMENT CORPORATION. March 3, 1958 [March 19, 1957], No. 6710/58. Class 38 (4). In a system for maintaining the pressure in a pressurized cabin at a desired value, air is supplied to the cabin under pressure and an exhaust valve for the cabin is automatically adjusted by a reversible A.C. motor under the control of A.C. signals responsive to cabin pressure and rate of change of cabin pressure. In Fig. 1, when cabin pressure deviates from a value determined by the setting of a knob 54 adjusting the bridge-type variable inductive pick-off 36 of a bellows 30 responsive to cabin pressure, A.C. signals are produced which are opposed to A.C. signals from the pick-off 34 of a bellows 28 responsive to rate of change of cabin pressure and applied to an amplifier 60, the output of which controls a two-phase reversible motor 62 adjusting a cabin exhaust valve 20 to correct the deviation. The signals from pick-off 36 reach a maximum value for small deviations of cabin pressure so that motor 62 operates to change cabin pressure at a rate corresponding to that maximum value which is adjustable manually by a potentiometer 56 controlling the energization of pick-off 36. The signals from amplifier 60 also control a motor 80 adjusting a second exhaust valve 21 for the cabin and the two exhaust valves are synchronized by further controlling motor 80 by the output of an amplifier 78 to which is applied synchronizing error signals developed by selsyns 70 and 74 associated with valves 20 and 21 respectively. A.C. signals produced by pick-off 38 of a bellows 32 when the difference between cabin and external pressure exceeds a predetermined value are also applied to amplifier 60 and they are of such magnitude and sense as to ensure movement of the valves to an open position to prevent undue stress on the cabin. Energization of relay 64 when the landing gear is operated prior to landing introduces a fixed A.C. voltage from potentiometer 68 in opposition to the signal from rate bellows 28 so that cabin pressure is equalized with external pressure at a predetermined rate. The pressure transducers are of the type described in Specification 882,786 (see Group XXXVIII).